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TZEX - Twilight Zone EXplorer

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Carbon Flux Through the Twilight Zone- New Tools to Measure Change

Schematic showing links between continuous remote sensing of surface ocean C uptake, twilight zone flux and deep ocean flux that are the focus of our current NSF funded project at Bermuda.
Building upon the success of our VERTIGO project, we continue to work to improve our understanding of how materials travel from the surface to the deep ocean. This pathway is called the "Biological Pump" (see Image 1 below) which refers to the combined activities that lead to a quick pathway for plant and animal debris (molts, fecal pellets, loose aggregated material) to sink as marine "snow" or a particle into the deep ocean (see Image 2 below). In the open ocean, this cycle is largely a biological one, though in some settings, transport of material delivered by dust may matter (TENATSO - Cape Verde time series project).

The "twilight zone" is a region of low light below the ocean's sunlit surface "euphotic" zone, and above the deep ocean boundary (around 1000m or 3000 feet). It is in this mysterious layer where most of the sinking particles of the world's ocean are consumed by the animals that live at depth.

In a new project starting in late 2006, we are designing an autonomous vehicle called the "Twilight Zone EXplorer" (TZEX) (see Image 3 below) to sample the ocean particle flux and make remote measurements in the twilight zone. Beginning in 2007, we will be starting to sample on a monthly basis at Bermuda, as part of the BATS (Bermuda Atlantic Time-Series) program using our existing particle flux collectors, the Neutrally Buoyant Sediment trap (see Image 4 below).

Image 1. The biological pump and processes regulating the flux of particles in the ocean. Carbon dioxide fixed during photosynthesis by phytoplankton in the upper ocean can be transferred below the surface mixed layer via three major processes: i) passive sinking of particles, ii) physical mixing of particulate and dissolved organic matter (DOM), and iii) active transport by zooplankton vertical migration. The sinking flux includes senescent phytoplankton, zooplankton fecal pellets, molts and mucous feeding-webs (e.g., larvacean houses) and aggregates of these materials. The sinking particle flux decreases with depth as aggregates are fragmented into smaller, non-sinking particles, decomposed by bacteria, and consumed and respired by zooplankton. This remineralization returns carbon and nutrients to dissolved forms. The structure of the planktonic community affects the composition and the sinking rates of particles. Particle size, form, density, and the content of biogenic minerals affect sinking and remineralization rates.

Image 2. Example of changes in fecal pellets from sediment traps at three depths in the subarctic North Pacific (K2). Note the primarily cylindrical copepod pellets at 150 m, the red, carnivore-produced pellets at 300 m, and the large, ellipsoid larvacean pellets at 500 m. (Wilson, Steinberg, and Buesseler, in prep.)

Image 3. Schematic of proposed Twilight Zone Explorer.

Image 4. WHOI NBST system being deployed.

TZEX Project Website
This site material is developed for NSF project PIs and those wishing to know a bit more about the details of the science, investigators, find a copy of the proposal, papers and other materials that are being generated.

Carbon Flux Through the Twilight Zone - New Tools to Measure Change, a poster presented by Stephanie Owens at the 2008 Ocean Sciences Meeting (PDF file).

Dehairs, F., A. de Brauwere, M. Elskens, U. Bathmann, S. Becquevort, S. Blain, P. Boyd, K. Buesseler, E. Buitenhaus, M. Gehlen, G. Herndl, C. Klass, R. Lampitt, D. Lefevre, U. Passow, H. Plous, F. Primeau, L. Stemmann and T. Trull (2008). Controls on Organic Carbon Export and Twilight Zone Remineralization: An Overview of the EUROCEANS Workshop . Oceanography, 21(3): 92-95.

Dehairs, F., A. de Brauwere and M. Elskens (2008). Organic Carbon in the Ocean's Twilight Zone. EOS, Transactions American Geophysical Union, 89 (38): doi:10.1029/2008EO380004.

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Figure from the Honolulu Advertiser article by Jan Ten Bruggencate.

Animation by Minette McCabe of The Honolulu Advertiser

General audience materials

WHOI 11/29/09 Image of the Day- Sunset on the RV Atlantic Explorer.

The Twilight Zone
An interview with Ken Buesseler on Episode 5 of Nature Publishing Group's Simply Science, part of Scitable: A Collaborative Learning Space for Science.

A Journey to the Ocean's Twilight Zone (pdf)
A conversation with marine biogeochemist Ken Buesseler: A torrent of particles rains down through the ocean's dimly lit regions, providing food for organisms below and sequestering some heat-trapping carbon dioxide from the atmosphere. A WHOI biogeochemist investigates what makes it into the ocean's twilight zone and what makes it out.

Swimming in the Rain (pdf)
Novel untethered vehicle catches 'marine snow' falling through the sea: At first, critics said it shouldn't be done. Then they wondered whether it could be done. Finally, WHOI scientists and engineers built an innovative device to capture a fundamental but still mysterious ocean phenomenon.

Ducklow, H.W., D.K. Steinberg, and K.O. Buesseler (2001). Upper Ocean Carbon Export and the Biological Pump (pdf) . Oceanography, 14(14): 50-58.

About Sediment Traps

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Selected Serious Science Publications
Buesseler, K.O. (1998). The de-coupling of production and particulate export in the surface ocean (pdf). Global Biogoechemical Cycles, 12 (2), 297-310.

Buesseler, K.O., Steinberg, D.K., Michaels, A.F., Johnson, R.J., Andrews, J.E., Valdes, J.R., and J.F. Price (2000). A comparison of the quantity and quality of material caught in a neutrally buoyant versus surface-tethered sediment trap. (pdf). Deep-Sea Research Part I, 47, 277-294.

Buesseler, K.O., A.N. Antia, M. Chen, S.W. Fowler, W.D. Gardner, Ö. Gustaffson, K. Harada, A.F. Michaels, M. Rutgers van der Loeff, M. Sarin, D.K. Steinberg and T. Trull (2006). An assessment of the use of sediment traps for estimating upper ocean particle fluxes (pdf). Submitted to Journal of Marine Research.

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Related Links
» BATS (Bermuda Atlantic Time-series Study)
» “Students & the Twilight Zone”
» NSF Carbon and Water Program
» Ocean Carbon and Biogeochemistry

U.S. National Science Foundation

We gratefully acknowledge the support of the U.S. National Science Foundation.

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